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41.
Although alkyl carbonic acids (ACAs) and their salts are referred to as instable species in aqueous medium, we demonstrate that a monoalkyl carbonate (MAC) can in fact be easily formed from bicarbonate and an alcohol even in the presence of a high amount of water. A CE system with two capacitively coupled contactless conductivity detectors (C?Ds) was used to obtain different parameters about these species and their reactions. Based on the mobilities obtained for a series of alcohols ranging from 1 to 5 carbons, the coefficients of diffusion and the hydrodynamic radii were calculated. When compared with the equivalent carboxylates, MACs have radii systematically smaller. Although the precise pK(a) values of the ACAs could not be obtained, because of the fast decomposition in acid medium, it was possible, for the first time, to show that they are below 4.0. This result suggests that the acidity of an ACA is quite similar to the first hydrogen of H?CO?. Using a new approach to indirectly calibrate the C?D, the kinetic constants and the equilibrium constants of formation were also obtained. The results suggest that the increase in the chain length makes the MACs less stable and more inert. 相似文献
42.
Sumitomo K Mayumi K Minamikawa H Masuda M Asahi T Shimizu T Ito K Yamaguchi Y 《Electrophoresis》2011,32(3-4):448-454
Although polyethylene oxide (PEO) offers several advantages as a sieving polymer in SDS capillary polymer electrophoresis (SDS-CPE), solution properties of PEO cause deterioration in the electrophoresis because PEO in solution aggregates itself, degrades into smaller pieces, and forms polymer-micelle complexes with SDS. We examined protein separation on SDS-CPE with PEO as a sieving matrix in four individual buffer solutions: Tris-CHES, Tris-Gly, Tris-Tricine, and Tris-HCl buffers. The solution properties of PEO as a sieving matrix in those buffers were examined by dynamic light scattering (DLS) and by surface tension. Preferential SDS adsorption onto PEO disturbed protein-SDS complexation and impaired the protein separation efficiency. Substantial adsorption of SDS to PEO was particularly observed in Tris-Gly buffer. The Tris-CHES buffer prevented SDS from adsorbing onto the PEO. Only Tris-CHES buffer achieved separation of six proteins. This study demonstrated efficient protein separation on SDS-CPE with PEO. 相似文献
43.
A mixture of ω-(4-cyanobiphenyl-4′-yloxy)alkyl methacrylate and 1,3,5-tris-(ω-methacryloyloxyalkyloxy)benzene was heated to
200 °C at 5–10 °C/min. A large, broad exothermic transition peak was observed by differential scanning calorimetry during
the first heating process. The transition indicated the formation of a networked polymer, which was then immersed for 24 h
in various nematic liquid crystals, such as 4-cyano-4′-pentylbiphenyl, to give liquid crystal gels. The networked polymers
and their corresponding liquid crystal gels exhibited different liquid crystal-isotropic transitions. The swelling behaviors
of the liquid crystal gels were compared with those of gels cross-linked with 1,6-hexanediol dimethacrylate, trimethylpropane
trimethacrylate, and pentaerythritol tetraacetate. The characteristics of liquid crystal gels cross-linked with 1,3,5-tris-(ω-methacryloyloxyalkyloxy)benzenes
were studied. 相似文献
44.
Soh N Tanaka M Hirakawa K Zhang R Nakajima H Nakano K Imato T 《Analytical sciences》2011,27(11):1069-1076
Sequential injection immunoassay systems for environmental measurements based on the selective immunoreaction between antigen and antibody were described. A sequential injection analysis (SIA) technique is suitable to be applied for the procedure of enzyme-linked immunosorbent assay (ELISA), because the washing and the addition of reagent solutions can be automated by using a computer-controlled syringe pump and switching valve. We selected vitellogenin (Vg), which is a biomarker for evaluating environmental risk caused by endocrine-disrupting chemicals in the hydrosphere, and linear alkylbenzene sulfonates (LAS) and alkylphenol polyethoxylates (APEO), which are versatile surfactants, as target analytes in the flow immunoassay systems. For Vg monitoring, SIA systems based on spectrophotometric, chemiluminescence, and electrochemical determinations were constructed. On the other hand, chemiluminescence determination was applied to the detection of LAS and APEO. For APEO, an SIA system combined with surface plasmon resonance (SPR) sensor was also developed. These new sequential injection immunoassay systems are expected to be useful systems for environmental analysis. 相似文献
45.
Terauchi T Kamikawai T Vinogradov MG Starodubtseva EV Takeda M Kainosho M 《Organic letters》2011,13(1):161-163
A stereoarray isotope labeled (SAIL) lysine, (2S,3R,4R,5S,6R)-[3,4,5,6-(2)H(4);1,2,3,4,5,6-(13)C(6);2,6-(15)N(2)]lysine, was synthesized by the "head-to-tail" conversion of SAIL-Glu, (2S,3S,4R)-[3,4-(2)H(2);1,2,3,4,5-(13)C(5);2-(15)N]glutamic acid, with high stereospecificities for all five chiral centers. With the SAIL-Lys in hand, the unambiguous simultaneous stereospecific assignments were able to be established for each of the prochiral protons within the four methylene groups of the Lys side chains in proteins. 相似文献
46.
A concise enantioselective total synthesis of 4'-ethynyl-2-fluoro-2'-deoxyadenosine (EFdA), an extremely potent anti-HIV agent, has been accomplished from (R)-glyceraldehyde acetonide in 18% overall yield by a 12-step sequence involving a highly diastereoselective ethynylation of an α-alkoxy ketone intermediate. 相似文献
47.
Monitoring the aggregation processes of amyloid-β using a spin-labeled, fluorescent nitroxyl radical
Mito F Yamasaki T Ito Y Yamato M Mino H Sadasue H Shirahama C Sakai K Utsumi H Yamada K 《Chemical communications (Cambridge, England)》2011,47(17):5070-5072
Amyloid nitroxyl radical (nitroxide) ligands were used to detect amyloid-β fibrils, the main constituents of senile plaques in Alzheimer's disease, using anisotropic ESR spectra, and were found to affect the aggregation process due to the radical functionality. These compounds have great potential as novel and multifunctional probes, combining spin labels, spin probes, and fluorescence probes. 相似文献
48.
Kataoka M Kouda Y Sato K Minakawa N Matsuda A 《Chemical communications (Cambridge, England)》2011,47(30):8700-8702
The synthesis of the 3'-deoxyapionucleoside 3'-triphosphates (apioNTPs) having the four natural nucleobases and their enzymatic incorporation into a DNA-DNA primer-template have been tried. Therminator DNA polymerase was shown to incorporate these apioNTPs effectively giving 43mer DNA-apioNA chimera. 相似文献
49.
Nobuyasu Itoh Takamitsu Otake Masahiko Numata Yoshie Aoyagi Mayumi Matsuo Takashi Yarita 《Analytical sciences》2008,24(9):1129-1133
To improve the extraction of polycyclic aromatic hydrocarbons (PAHs) from sediment samples, we optimized the conditions of pressurized liquid extraction (PLE). The yields increased as the extraction temperature increased from 100 to 190 degrees C, but the effect of increasing pressure (from 15 to 20 MPa) was small. Parameters of 190 degrees C and 20 MPa, near the maximum of the equipment, gave the highest yield. Under these conditions, the yields of 17 PAHs were 1.5 - 34 times those obtained by the Japanese official method (shaking and ultrasonic extraction with acetone at room temperature). 相似文献
50.
Yoshitaka Ishii Koichi Hirao Takehiko Terao Tsutomu Terauchi Makoto Oba Kozaburo Nishiyama Masatsune Kainosho 《Solid state nuclear magnetic resonance》1998,11(3-4):169-175
A solid state NMR method is presented for determination of a backbone dihedral angle φ in peptides, being based on the previously reported method, relayed anisotropy correlation (RACO) NMR [Y. Ishii et al., Chem. Phys. Lett. 256 (1996) 133]. In the present method, the
and the
dipolar tensors in the
system are two-dimensionally (2D) correlated via polarization transfer from
to
under magic angle spinning (MAS). This method was applied to N-acetyl
,
-valine, and the H–C–N–H dihedral angle was determined to be 154.0±1.4° or 206.0±1.4°, the former agreeing with the X-ray value of 154±5°. 相似文献